250 narrowcase rear axle orientation info needed

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double diamond
Posts: 555
Joined: Thu Apr 28, 2011 1:20 am

Re: 250 narrowcase rear axle orientation info needed

Postby double diamond » Mon May 11, 2020 9:34 pm

You have a Grimeca speedo drive plate assembled to a Campagnolo hub. The Campagnolo plate doesn’t have the faux air scoop. I thought this might be the issue but the width of the two plates is the same. Same dimension with the brake plates C vs.G as well (the Campagnolo brake plate is different but not as easy to distinguish between the two). But the gap between the hub and brake plate tells me you have the brake plate positioned too far from the hub. Without delving into the pros and cons of shimming, the parts catalog shows no shims between the hub bearings and the left/right plates. The only thing that determines the position of the plates relative to the hub is the bearing spacer inside the hub, which is prone to deformation. If you have shims installed between the wheel bearings and plates, you are giving up axle length. All NC singles from early 4 speeds to the end of production show the same axle in the catalog (0270.77.330) but there are differences. The early axles were chrome plated and had a threaded hole in the shoulder. The later axles are zinc plated with no threaded hole. Both types measure ~175mm along the smaller diameter length. But, there are other, similar axles likely from other manufacturers that look identical but with lengths that are shorter or longer. Since you’re assembling a box of parts, check the axle length and the shimming. An assembled Grimeca hub I have at hand is 123mm between the plates.

Jordan
Posts: 1380
Joined: Fri Dec 24, 2010 11:29 am

Re: 250 narrowcase rear axle orientation info needed

Postby Jordan » Mon May 11, 2020 9:43 pm

In Commodore's last photo there is a black washer between the fork leg and cover plate.
Should that be there?

double diamond
Posts: 555
Joined: Thu Apr 28, 2011 1:20 am

Re: 250 narrowcase rear axle orientation info needed

Postby double diamond » Mon May 11, 2020 10:07 pm

As Jon noted “when the axle nut is tightened, the axle pulls the entire hub to the left”. I can’t tell if that is a spacer on the right or a gap between the fork slider and the speedo plate. If it’s a gap, good; if it’s a spacer, bad. A spacer would only shorten the length of the axle between the axle shoulder and the exposed thread beyond the left fork slider, which is the problem in question. The shoulder of the axle should butt up against the speedo plate.

Jordan
Posts: 1380
Joined: Fri Dec 24, 2010 11:29 am

Re: 250 narrowcase rear axle orientation info needed

Postby Jordan » Tue May 12, 2020 11:37 am

That evident washer (if it exists! I think it does - zoom in to check it out) might have an inner diameter to match either the large or small diameter of the axle.
In either case I agree that it ought not to be there.
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tobydmv
Posts: 88
Joined: Wed Apr 16, 2014 4:59 am

Re: 250 narrowcase rear axle orientation info needed

Postby tobydmv » Wed May 13, 2020 1:49 am

I have a similar problem with a mismatched hub but it appears my axle is way too long on the R or speedo side. I also have both speedo drive plates so measured them. The Campy(or whoever made it) plate without the fake air scoop is 2-3mm shorter. If you add that to the width of that washer or spacer you might get your missing threads. One thing to also consider is the depth of the bearings in the hub. If you rebuilt the hub with new bearings its possible to press them in too far. I think the spacer should be movable with your finger and the bearing dust seal should be just inside the hub flange.


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